1. Technical Field
The invention relates to mercaptoamidine derivatives, compositions comprising such compounds, methods for making the compounds, and methods of treating conditions and disorders using such compounds and compositions.
2. Description of Related Technology
Histamine is a well-known modulator of neuronal activity. At least four types of histamine receptors have been reported in the literature, typically referred to as histamine-1, histamine-2, histamine-3, and histamine-4. The class of histamine receptor known as histamine-3 receptors is believed to play a role in neurotransmission in the central nervous system.
The histamine-3 (H3) receptor was first characterized pharmacologically on histaminergic nerve terminals (Arrang J M, et al. Nature 1983, 302: 832-837), where it regulates the release of neurotransmitters in both the central nervous system and peripheral organs, particularly the lungs, cardiovascular system and gastrointestinal tract. H3 receptors are thought to be disposed presynaptically on histaminergic nerve endings, and also on neurons possessing other activity, such as adrenergic, cholinergic, serotoninergic, and dopaminergic activity. The existence of H3 receptors has been confirmed by the development of selective H3 receptor agonists and antagonists (Arrang J M, et al. Nature 1987, 327: 117-123; Leurs R and Timmerman H eds. “The Histamine H3 Receptor: a Target for New Drugs,” Elsevier (1998)).
The activity at the H3 receptors can be modified or regulated by the administration of H3 receptor ligands. The ligands can demonstrate antagonist, inverse agonist, agonist, or partial agonist activity. H3 receptors have been linked to conditions and disorders related to memory and cognition processes, neurological processes, cardiovascular function, and regulation of blood sugar, among other systemic activities. Although various classes of compounds demonstrating H3 receptor-modulating activity exist, it would be beneficial to provide additional compounds demonstrating activity at the H3 receptors that can be incorporated into pharmaceutical compositions useful for therapeutic methods.